The present invention relates to a paper-feeding roller. Particularly, the present invention relates to a paper-feeding roller for use in a paper-feeding mechanism of a printing apparatus, a color facsimile, and the like.
More particularly, the present invention relates to a paper-feeding roller which can be preferably used in a printing apparatus of ink jet type and has improved wear resistance when it rubs against a separation pad at the time of exhaustion of paper.
The paper-feeding roller is used in a paper-feeding mechanism of an office appliance such as the printer, the color facsimile, a copying machine, an ATM, and the like. Normally, EPDM (ethylene-propylene-diene copolymer), natural rubber, urethane rubber, chloroprene rubber, polynorbornane, and the like are used for the paper-feeding roller. Because the paper-feeding roller is used to feed paper, a film, and the like, the paper-feeding roller is required to have a high friction coefficient to allow it to have a high paper-feeding force. The paper-feeding roller is also required to have a superior wear resistance to withstand continuous paper-feeding.
Various proposals have been made to provide a paper-feeding roller having a high friction coefficient and a superior wear resistance. For example, the paper-feeding roller proposed in Japanese Patent Application No.9-88048 is composed of rubber having a low loss tangent (elastic hysteresis loss: tan xcex4) to reduce its hardness to thereby restrain the paper-feeding roller from slipping on paper and improve its wear resistance.
In recent years, household printers and facsimiles have come into popular use. Because these printing apparatuses are for personal users, they are required to be inexpensive. Thus, as a printing method, ink jet type is normally adopted for the household printing apparatuses.
In the paper-feeding mechanism of the ink jet type printing apparatus, when printing paper in a paper-feeding tray unit is exhausted, the paper-feeding roller is forcibly idled over a separation pad. The exhaustion of the printing paper is detected by the idling of the paper-feeding roller. The detection method eliminates the need for providing the paper-feeding mechanism with a member for detecting the exhaustion of the printing paper. Thus, the detection method has an advantage of reducing the cost of the printing apparatus of ink jet type.
However, in the printing apparatus of ink jet type, when the paper-feeding roller idles, the paper-feeding roller rubs against the separation pad and is worn.
The inventor of the above-described paper-feeding roller paid attention to the restraining of the paper-feeding roller from slipping on the paper to improve its friction coefficient and wear resistance. Thus, the paper-feeding mechanism of the ink jet type printing apparatus cannot prevent the paper-feeding roller from being worn strongly owing to rubbing of the paper-feeding roller against the separation pad.
That is, in improving the wear resistance of the paper-feeding roller, the inventor has not paid attention to the fact that the paper-feeding roller is forcibly idled with the paper-feeding roller rubbing against the separation pad. Therefore, the paper-feeding roller does not have a sufficient wear resistance.
Consequently, when the conventional paper-feeding roller is adopted in the ink jet type printing apparatus, the paper-feeding roller is worn strongly because the paper-feeding roller rubs more strongly against the separation pad than against paper.
When the wear resistance is insufficient, powder generated when the paper-feeding roller is worn attaches the surface of the paper-feeding roller and the powder attaches to paper in subsequent printing. When the powder attaches to the paper, an image formation is difficult and the powder separates from the paper after an image is formed thereon to form a blank portion on the formed image.
The present invention has been made in view of the problem. Thus, it is an object of the present invention to provide a paper-feeding roller having superior wear resistance and not generating powder when the paper-feeding roller rubs against a separation pad.
To achieve the object, the present invention provides a paper-feeding roller, made of a cylindrical elastic material, with the paper-feeding roller mounted on a core. A friction coefficient (xcexc) of the paper-feeding roller is set not less than 1.5. The friction coefficient (xcexc) of the paper-feeding roller, a tensile elongation E (%) thereof, and a fracture-time strength T (MPa) thereof are set to the following relationship:
15 greater than (Exc3x97T)/(xcexcxc3x97100)xe2x89xa75
The reason friction coefficient (xcexc) of the paper-feeding roller is set not less than 1.5 is because if the friction coefficient (xcexc) is less than 1.5, in an ink jet type printing apparatus in which various types of paper are fed, there occurs a situation in which the paper-feeding roller cannot feed paper because of its insufficient paper-feeding force.
According to the present invention, each of the tensile elongation (E) of the paper-feeding roller and its fracture-time strength (T) is set high. The friction coefficient (xcexc) of the paper-feeding roller is also set high so that a value P=(Exc3x97T)/(xcexcxc3x97100) (MPa) is set not less than 5 nor more than 15.
Because the value P is set not less than 5 nor more than 15, the paper-feeding roller maintains a high friction coefficient, has improved wear resistance, hardly generates powder when it rubs against a separation pad, and does not delay feeding paper because it has a high paper-feeding force. That is, if the value P is less than five, the tensile elongation (E) of the paper-feeding roller and its fracture-time strength (T) become low, and a breaking strength (Exc3x97T) which is an index of its wear resistance becomes also low, and its wear resistance deteriorates because its friction coefficient becomes high.
If the value P is less than 15, its compression permanent set becomes high and its paper-feeding force becomes low.
Supposing that the breaking strength (tensile elongation (E)xc3x97fracture-time strength (T)) is low and that the friction coefficient of the paper-feeding roller used for the printing apparatus of ink jet type is low, the amount of powder generated by abnormal abrasion is small and the generated powder hardly attaches to paper during idling of the paper-feeding roller. Thus, printing is not adversely affected by the paper-feeding roller.
However, if the friction coefficient of the paper-feeding roller is less than 1.5, the paper-feeding roller has an insufficient paper-feeding force, as described above. Thus, the value P is set to the above-described range by setting its friction coefficient and the breaking strength (Exc3x97T) high.
From the above-described standpoint, the tensile elongation E (%) is favorably in the range of 100 to 800 and more favorably in the range of 150 to 700. The fracture-time strength T is favorably in the range of 1.5 to 8.0 and more favorably in the range 2.5 to 5.0. The breaking strength expressed by (E)xc3x97(T) is favorably in the range of 800 to 2000 and more favorably in the range of 800 to 1500. The friction coefficient (xcexc) is favorably in the range of 1.5 to 3.5 and more favorably in the range of 1.5 to 3.0.
In the case where the paper-feeding roller is used for an ink jet type printing apparatus, the friction coefficient (xcexc) of the paper-feeding roller is set to the range of 1.5 to 3.5. In the case where the paper-feeding roller is used for a printing apparatus not of the ink jet type, the friction coefficient (xcexc) thereof is set to the range of 2.0 to 3.0.
It is preferable that the elastic material of the paper-feeding roller is composed of a thermoplastic elastomer composition. In this case, it is easy to adjust the value P to the above-described range.
Preferably, a diene-containing polymer is dynamically cross-linked with a resin-cross-linking agent, with the diene-containing polymer being mixed with a thermoplastic elastomer to form the elastic material of a composition containing a matrix consisting of the thermoplastic elastomer and the cross-linked diene-containing polymer dispersed in the form of particles in the matrix.
As the diene-containing polymer which is dispersed in the form of particle, EPDM, natural rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber, and polynorbornene can be used. The weatherable EPDM is most favorable of these polymers.
As the thermoplastic elastomer which forms the matrix, it is possible to use styrene thermoplastic elastomer, olefin thermoplastic elastomer, urethane thermoplastic elastomer, ester thermoplastic elastomer, and amide thermoplastic elastomer. These thermoplastic elastomers are used independently or as a mixture of two of them. The styrene thermoplastic elastomer and the olefin thermoplastic elastomer (for example, propylene thermoplastic elastomer) are most favorable of these thermoplastic elastomers, because the paper-feeding roller containing these two thermoplastic elastomers has a low hardness and compression permanent set.
Hydrogenated styrene thermoplastic elastomer is most favorable of the styrene thermoplastic elastomers. Because an intermediate block of the hydrogenated styrene thermoplastic elastomer is hydrogenated, the double bond disappears and thus the hydrogenated styrene thermoplastic elastomer is not cross-linked during the dynamic cross-linking. Therefore, it is easy to plasticize the thermoplastic elastomer composition after the dynamic cross-linking is performed. As the hydrogenated styrene thermoplastic elastomer, it is possible to use styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), styrene-ethylene-styrene copolymer (SES), styrene-ethylene/propylene-styrene copolymer (SEPS), and styrene-ethylene/butadiene-styrene copolymer (SEBS). The olefin thermoplastic elastomer does not have a double bond either. Thus, it is easy to plasticize a thermoplastic elastomer composition containing the olefin thermoplastic elastomer.
Instead of these thermoplastic elastomers or in combination therewith, the following thermoplastic resins can be used as the thermoplastic polymers forming the matrix: chlorinated polyethylene, polyvinyl chloride, polyolefin, polyurethane, polyester, polyester-polyether, polyamide, ionomer resin, EEA resin, and ethylene-vinyl acetate copolymer.
As the thermoplastic elastomer forming the matrix, it is preferable to use a substance having a comparatively high molecular weight to easily set the parameter P of the paper-feeding roller to the above-described range.
It is preferable to use the styrene-ethylene/propylene-styrene copolymer (SEPS) having a molecular weight of favorably not less than 200000 and more favorably not less than 300000. It is also preferable to mix polypropylene (PP) having a comparatively high molecular weight with the styrene-ethylene/propylene-styrene copolymer (SEPS).
It is preferable that the weight ratio of the thermoplastic elastomer to the diene-containing polymer is not less than {fraction (3/7)} nor more than {fraction (6/4)}. If the weight ratio is less than the lower limit, it is difficult for the thermoplastic elastomer to be present as the matrix. Thus, processability such as extrusion and pelletizing becomes poor. If the weight ratio is more than the upper limit, the rubber component becomes less. Thus, it is difficult to impart desired flexibility to the paper-feeding roller.
As the thermoplastic elastomer which forms the matrix, the styrene-ethylene/propylene-styrene copolymer (SEPS) having a molecular weight of not less than 200000 is mixed with the polypropylene (PP) at a ratio of 2:1 to 4:1. The thermoplastic elastomer consisting of the SEPS and the PP and the diene-containing polymer consisting of the EPDM are mixed with each other at a ratio of 3:7 to 6:4. Oil is mixed with a thermoplastic elastomer composition consisting of the SEPS, the PP, and the EPDM at a ratio of 1.5:1 to 2:1.
As the resin-cross-linking agent, a substance consisting of a halogenated addition condensation resin is used or a mixture of an addition condensation resin and a halogenating substance is used.
That is, after the reaction in which the dynamic cross-linking occurs, a by-product is hardly generated from the diene-containing polymer. Thus, the diene-containing polymer is preferably used as the resin-cross-linking agent. In particular, the substance consisting of the halogenated addition condensation resin is used or the mixture of the addition condensation resin and the halogenating substance is used as the resin-cross-linking agent, because these substances activate the cross-linking and allow the characteristic value P to be set to the above-described range easily.
The halogenating substance may be metal halide or resin halide. As the metal halide, it is possible to use tin chloride such as stannic chloride, iron chloride such as ferric chloride, cupric chloride such as copper chloride. As the resin halide, chlorinated polyethylene and the like can be used. These halogenating substances can be used independently or as a mixture of two or more thereof.
Favorably, the resin-cross-linking agent contains halogenated alkylphenol formaldehyde resin. It is favorable to add 15-3 parts by weight of the halogenated alkylphenol formaldehyde resin and more favorable to add 10-5 parts by weight thereof to 100 parts by weight of the diene-containing elastomer.
Most favorably, the resin-cross-linking agent contains the halogenated alkylphenol formaldehyde resin and alkylphenol formaldehyde resin mixed therewith at the ratio of 35:100 to optimize the cross-linking.